Re: It all depends
From what I've seen, the majority of NHS computers are essentially just running a terminal emulator anyway. I don't see how XP is any worse than anything else at hosting that.
Also, end of support doesn't mean that suddenly it's all open for anyone to gain access. It just means that new holes won't be patched. It will still need a concerted attack to breach the perimeter defences before they can even start to attack individual PCs.
Of course, I'm assuming that the sysadmins have already removed as much of IE as they can and certainly hidden the icons for it!